1. Field of the Invention
The present invention relates to a nonaqueous-electrolyte battery in which terminals electrically connected to a positive and a negative electrode are hemetically sealed (hereinafter referred to as simply "sealed") in an opening hole of a cover plate of a battery case.
2. Description of the Related Art
The nonaqueous-electrolyte battery to which the present invention is applied should not be particularly limited. Now, as an example, an explanation will be given of a typical structure of a large-scale large-capacity elliptical-cylindrical nonaqueous battery 1. As seen from FIG. 4, a power generating element 1 of the nonaqueous-electrolyte battery is composed of a belt-shaped positive electrode (cathode) 1a and a belt-shaped negative electrode (anode) 1b which are wound in an elliptical-cylinder through a belt-shaped separator 1c. These positive electrode 1a and negative electrode 1b are wound in a manner displaced vertically little by little so that the lower end of the positive electrode 1a protrudes downwards and the upper end of the negative electrode 1b protrudes upwards. A negative collector 5 is hermetically connected (hereinafter referred to as simply "connected") to the upper end of the negative electrode 1b of the power generating element 1 which protrudes upwards. The negative collector 5 is made by stamping a metallic plate and folded to form slits. The upper end of the negative electrode 1b is inserted in and connected to the respective slits by caulking or welding. A negative electrode terminal 4 is connected to the negative collector 5 by caulking or welding so that it protrudes upward. A positive collector 3 is connected to the lower end of the positive electrode 1a of the power generating element 1 which protrudes downwards. The one end of the positive collector 3 is extended to the negative collector 5 along the power generating element 1 to reach the upper side thereof. A positive electrode terminal 2 is connected to the positive collector 3 by caulking or welding.
The power generating element 1, to which the positive collector 3 and the negative collector 5 are connected, is housed within an elliptical-cylindrical case body 8a of a battery case 8 as shown in FIG. 5. The positive electrode terminal 2 and negative electrode terminal 4 which are connected to the positive collector 3 and negative collector 5 are passed through the opening holes located at two positions of the elliptical-cylindrical cover plate 8b. These electrode terminals 2 and 4 are insulatedly sealed by insulating materials between themselves and the opening holes. The cover plate 8b is fit in the upper opening of the case body 8a and its periphery is sealed by welding. Thus, the battery in which the positive electrode terminal 2 and negative electrode terminal 4 protrude upward from the opening holes of the cover plate 8b of the battery case 8 is constructed.
These electrode terminals 2 and 4 can be insulatedly sealed by means of the techniques of glass hermetic sealing and ceramic hermetic sealing.
However, these techniques have the following defects. For example, where the positive electrode 2 is formed by the glass hermetic sealing technique, as shown in FIG. 6, glass is molten between the positive electrode terminal 2 and cover plate 8b in a furnace at a high temperature of about 300 to 600.degree. C., and hardened to form a glass hermetic seal 7. However, in the state where the power generating element 1 is connected to the positive electrode terminal 2 as described above, actually, the working of forming the glass hermetic seal cannot be carried out. This is because the power generating element 1 cannot withstand the above high temperature and hence the glass cannot be molten. This applies to the case where the negative electrode terminal 4 is formed.
Further, in the battery manufactured by means of the ceramic hermetic seal technique, as seen from FIGS. 7, 8, 9 and 10, the positive electrode terminal 2 and the negative electrode terminal 4 are insulatedly secured to the battery case through the ceramic material 9, respectively. Each of these positive and negative electrode terminals 2 and 4 with the ceramic material 9 fit thereover is inserted in the opening hole of the cover plate 8b. In this state, a metallic brazer (brazing metal) 10a is secured between each electrode terminal 2, 4 and the ceramic material 9, and a metallic brazer (brazing metal) 10b is secured between the ceramic material 9 and the opening hole of the cover plate 8b. The metallic brazers 10a, 10b are molten in a furnace at a high temperature of about 1000.degree. C. and hardened so that sealing is made between each electrode terminal 2, 4 and the ceramic material 9, and between the ceramic material 9 and the opening hole of the cover plate 8b. However, in the state where the power generating element 1 is connected to the positive electrode terminal 2 or the negative electrode terminal 4 as described above, actually, the working of sealing/securing cannot be carried out. The reason therefor is the same as the case of using the glass hermetic sealing technique.
As described above, the power generating element 1 cannot be exposed to the environment at a high temperature. Therefore, in the conventional art, the following working of connection is carried out. The positive and negative electrode terminals 2 and 4 are previously insulatedly sealed to the cover plate 8b by means of the glass hermetic sealing or ceramic hermetic sealing technique. Thereafter, the positive collector 3 and negative collector 5 which are connected to these positive electrode 2 and the negative electrode terminal 4 are connected to the power generating element 1. Otherwise, the positive electrode terminal 2 and negative electrode terminal 4 are connected to the positive collector 3 and the negative collector 5 which are connected to the power generating element 1.
Therefore, conventionally, such a working of connection must be carried out by caulking or welding with a special jig inserted in a lower gap of the cover plate 8b. In this case, the workability is very poor. In addition, the reliability of the connecting portion is deteriorated owing to such a difficult working. Further, there was also a problem that a redundant space is required in order to assure the space for working and the battery capacity is reduced correspondingly.
Particularly, in a cylindrical or elliptical-cylindrical battery, the connection among the collector and terminal must be carried out in a small space at the end in an axial direction of the power generating element by caulking or welding. The poor workability in this case was very problematic.
For the reasons described above, conventionally, in many cases, without using the glass hermetic sealing technique or ceramic sealing technique, each of the positive electrode terminal 2 and the negative electrode terminal 4 is passed through the opening hole of the cover plate 8b through a sealing member such as an O-ring or a washer of synthetic resin and tightened by a nut so that it is insulatedly sealed. However, the sealing member such as the O-ring or washer of synthetic resin is likely to deteriorate with time. Therefore, there was a problem that the hermeticity is attenuated with use and hence the electrolyte may leak.
The conventional ceramic hermetic sealing technique has a problem of corrosion of a metallic brazer. In the case of the Ni--Cd battery or Ni--MH battery, as the metallic brazer 10a, 10b for brazing the ceramic material 9, silver (Ag) brazer or silver-copper (Ag--Cu) brazer (containing Cu of 15 to 40%) was used. However, when such an Ag brazer or Ag--Cu brazer is used in the nonaqueous-electrolyte battery, the metallic brazer 10a, 10b, which serves to braze the ceramic material 9 onto the negative electrode terminal 4, is brought into contact with the nonaqueous electrolyte. Thus, it might corrode owing to an alloying reaction with the alkaline metal such as lithium so that the hermeticity is lost. This might shorten the cycle life and calendar life. In order to restrain the corrosion of the brazing material, the copper brazer can be also used. However, it is very difficult to braze the ceramic material to the negative electrode terminal of Cu or Cu alloy using the Cu brazer because the melting points of the negative electrode terminal and Cu brazer are approximate to each other.